Electrical motors often use wound stators: this is particularly true for AC motors (both asynchronous and synchronous) as well as DC brushless motors. The winding of these stators can be quite difficult (and costly) when the motor diameter is small in comparison to its length. Such long, thin motors are commonly used in electric submersible pumps (ESPs) of the type used in the oil industry to provide artificial lift in wells that do not have enough pressure to produce to the surface.
Stators are typically constructed from a stack of thin metal plates to limit the strength (and associated loss) from eddy currents. The thickness of these plates is typically in the range of 1 millimeter (or less). It may therefore take 10,000 plates for the construction of long ESP motors and these plates need to be properly aligned so that the wire channels are properly defined. FIG. 1 shows a motor construction comprising a stator 10 formed from a stack of such plates with holes defining the wire channels in which windings 12 are provided. A rotor 14 is located in a central cavity.
The winding of these long motor stators is difficult as the wires run in long narrow slots formed in the stack of stator metal laminations. The wire is typically passed through the slots by pulling it with a long needle: this process is slow and tedious. The filling of the slots by the wires is also often limited, reducing the optimum usage of the motor section for high magnetic flux and optimum heat transfer.
With these long stators, the reaction torque from the stator is often transmitted to the motor housing by friction. The laminations are pre-compressed axially at high load. This load is supported by large circlips which are inserted in a circumferential groove in the housing.
This construction technique of such stators is found with a wide variety of motors, such as three-phase AC motors or certain DC (brushless) motors.